decoder/sidplay: Fix empty album names by using the SID name field

SID files are generally collections of tunes, so a SID name field makes
sense as an MPD album. The SID tune information list (STIL) has name
and title fields for individual tunes, when such are known, but MPD is
currently not using the STIL.

NEWS

@@ -11,6 +11,7 @@ ver 0.22 (not yet released)
   - iso9660: support seeking
 * decoder
   - sidplay: add option "default_genre"
+  - sidplay: map SID name field to "Album" tag
 * filter
   - ffmpeg: new plugin based on FFmpeg's libavfilter library
   - hdcd: new plugin based on FFmpeg's "af_hdcd" for HDCD playback

src/decoder/plugins/SidplayDecoderPlugin.cxx

@@ -510,16 +510,18 @@ static void
 ScanSidTuneInfo(const SidTuneInfo &info, unsigned track, unsigned n_tracks,
 		TagHandler &handler) noexcept
 {
-	/* title */
-	const auto title = GetInfoString(info, 0);
+	/* album */
+	const auto album = GetInfoString(info, 0);
+
+	handler.OnTag(TAG_ALBUM, album.c_str());
 
 	if (n_tracks > 1) {
 		const auto tag_title =
 			StringFormat<1024>("%s (%u/%u)",
-					   title.c_str(), track, n_tracks);
+					   album.c_str(), track, n_tracks);
 		handler.OnTag(TAG_TITLE, tag_title.c_str());
 	} else
-		handler.OnTag(TAG_TITLE, title.c_str());
+		handler.OnTag(TAG_TITLE, album.c_str());
 
 	/* artist */
 	const auto artist = GetInfoString(info, 1);